vendor/llvm/llvm-trunk-r303291

1 files changed, 21 insertions, 7 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index caf5cb497a715..0ccee175abfb5 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -13087,14 +13087,28 @@ SDValue DAGCombiner::visitSTORE(SDNode *N) {
     }
   }
 
-  // If this is a store followed by a store with the same value to the same
-  // location, then the store is dead/noop.
   if (StoreSDNode *ST1 = dyn_cast<StoreSDNode>(Chain)) {
-    if (ST1->getBasePtr() == Ptr && ST->getMemoryVT() == ST1->getMemoryVT() &&
-        ST1->getValue() == Value && ST->isUnindexed() && !ST->isVolatile() &&
-        ST1->isUnindexed() && !ST1->isVolatile()) {
-      // The store is dead, remove it.
-      return Chain;
+    if (ST->isUnindexed() && !ST->isVolatile() && ST1->isUnindexed() &&
+        !ST1->isVolatile() && ST1->getBasePtr() == Ptr &&
+        ST->getMemoryVT() == ST1->getMemoryVT()) {
+      // If this is a store followed by a store with the same value to the same
+      // location, then the store is dead/noop.
+      if (ST1->getValue() == Value) {
+        // The store is dead, remove it.
+        return Chain;
+      }
+
+      // If this is a store who's preceeding store to the same location
+      // and no one other node is chained to that store we can effectively
+      // drop the store. Do not remove stores to undef as they may be used as
+      // data sinks.
+      if (OptLevel != CodeGenOpt::None && ST1->hasOneUse() &&
+          !ST1->getBasePtr().isUndef()) {
+        // ST1 is fully overwritten and can be elided. Combine with it's chain
+        // value.
+        CombineTo(ST1, ST1->getChain());
+        return SDValue();
+      }
     }
   }